An inflammatory response characterized by leukocyte emigration and increased vascular permeability to fluids and proteins is seen in a number of common disease states including infection, atherosclerosis, acute respiratory distress syndrome, and immune complex diseases. To examine leukocyte migration and alterations in permeability across an endothelial cells (EC) barrier, I have cultured human EC monolayers on a substrate of human amnion. I have measured the permeability of these monolayers and changes in EC cytosolic free calcium ((Ca++)i) during human neutrophil (PMN) migration across such EC monolayers. Transendothelial PMN migration occurs in response to chemoattractants and does not alter the permeability of EC monolayers. Both histamine, which increases EC monolayer permeability, and PMN migration across an EC monolayer induce increases in EC (Ca++)i and changes in EC shape. The goals of the proposed research are: 1) to determine whether PMN surface proteins and/or secretory products initiate EC (Ca++)i changes using antibodies against leukocyte surface proteins and supernatants derived from activated PMN, 2) to examine the role of EC (Ca++)i changes in mediating transendothelial PMN migration or permeability changes by examining the effect of buffering EC (Ca++)i changes on these events, 3) to search for EC myosin light chain phosphorylation or actin rearrangement in stimulated EC as evidence that migrating leukocytes and agonists such as histamine induce EC cytoskeletal changes as a basis for altering EC monolayer permeability, and 4) to examine the relationship between (Ca++)i and changes in the permeability of endothelial and epithelial monolayers by determining if substances which increase the permeability EC monolayers affect EC (Ca++)i and if PMN migration across monolayers of epithelial cells alter epithelial (Ca++)i.